Wastes as support materials for the development of biological barriers for landfill liners.

Abstract

Biological clogging permits reducing the permeability of waste materials, which can be used in the design of barriers for retaining contaminants, promoting environmental protection and circularity. The present study evaluated using construction and demolition waste (CDW) and tire waste (TW) as support materials for developing biobarriers within the landfill design. The experimental setup consisted of vertically positioned PVC columns, filled with CDW, its mixture with tire waste (CDW/TW) or with anaerobic biomass (in CDW). The columns were fed with raw leachate collected from an active municipal landfill in Madrid, Spain, (dissolved organic carbon (DOC) 278 ± 150 mg/L, pH 7.4 ± 0.4, electrical conductivity (EC) 14,013 ± 5218 µS/cm, oxidation-reduction potential (ORP) -126 ± 100 mV). Head loss and flow measurements enabled calculating the permeability of the materials over time (Darcy's law). Inlet and outlet samples were collected daily (pH, EC, ORP, temperature) and biweekly (cations, anions, trace elements, DOC). The results showed a reduction in hydraulic conductivities of 2-3 orders of magnitude, achieving better results for the CDW/TW columns (10-7 m/s in 170 days), possibly due to the hydrophobicity of tire, enhancing biofilm adhesion. An exponential correlation showed that hydraulic conductivities of 10-9 m/s (the minimum legal limit for compacted clay liners under waste landfills) can be reached before 420 days of operation. Physicochemical analysis indicated sulfate reduction, possibly contributing to the precipitation of heavy metals into sulfide minerals within the biobarrier. The incorporation of waste materials in landfill liners can reduce contamination in the medium and long terms and contribute to the circular economy.